Life in the sublittoral zone of long-lived Lake Pannon: paleontological analysis of the Upper Miocene Szák Formation, Hungary

Abstract

Life and depositional environments in the sublittoral zone of Lake Pannon, a large, brackish Paratethyan lake from the Late Miocene, were reconstructed from fossils and facies of the Szák Formation. This formation is exposed in several, roughly coeval (9.4-8.9 Ma) outcrops, located along strike of the paleo-shelf-break in northwestern Hungary. The silty argillaceous marl of the formation was deposited below storm wave base, at 20-30 to 80-90 m water depth. The abundance of benthic organisms indicates that the bottom water was usually well oxygenated. Interstitial dysoxia, however, may have occurred immediately below the sediment-water interface, as evidenced by occasional preservation of trace fossils such as Diplocraterion. The fauna comprised endemic mollusks, including brackish cockles of the subfamily Lymnocardiinae, dreissenid mussels (Congeria), and highly adapted, uniquely large-sized deep-water pulmonate snails (planorbids and lymnaeids). Ostracods were dominated by endemic species and, in some cases, endemic genera of candonids, leptocytherids, cypridids, and loxoconchids. Fish remnants include a sciaenid otolith and the oldest skeletal occurrence of Perca in Europe. The phytoplankton comprised exclusively endemic coccolithophorids, mostly endemic dinoflagellates (prevailingly Spiniferites), and cosmopolitan green algae. The Late Miocene fauna and flora of Lake Pannon were in many ways similar to the modern Caspian biota, and in particular cases can be regarded as its precursor.

Upper Miocene Pannonian sediments from Belgrade (Serbia): new evidence and paleoenvironmental considerations

“…Similar observations and discussion about environmental changes and diversification of Late Miocene Cyprideis from the Lower Pannonian of the Styrian Basin have been reported by Gross (2008) and Gross et al (2008). Analogous forms of Amnicythere species are living in the sublittoral zones of the Black Sea and the Caspian Sea in brackish environments as well as in more freshwater bays (Cziczer et al 2009). Similar to this, recent Cypria species are generally freshwater forms but can tolerate mesohaline conditions (Meisch 2000;Starek et al 2010).…”

Palaeobiology, palaeoecology and stratigraphic significance of the Late Miocene cockle Lymnocardium soproniense from Lake Pannon

“…It points to a drastically increased rate of sediment input, which can be the result of either development of a delta entry nearby or a lake-level fall (or their combined effect). The clay is assigned to the Szák Formation (see Cziczer et al 2009 and references therein), whereas the gravelly white sand belongs to the Kálla Formation (see Csillag et al 2010 and references therein).…”

“…There are no indications of storm-or gravity-induced currents, a fact that may point to a flat depositional surface far away from sediment input. Water depth is difficult to reconstruct, but studies of the Szák Formation elsewhere and comparisons with the present-day Caspian Sea as an analogue of Lake Pannon suggest that the sublittoral argillaceous marl was deposited at 20-30 to ?80 m water depth (Korpás-Hódi 1983;Cziczer et al 2009). L. soproniense becomes less common and finally disappears from the record as sediment input increased and water depth decreased up to and even above the wave-base.…”

Turbidites as indicators of paleotopography, Upper Miocene Lake Pannon, Western Mecsek Mountains (Hungary)

“…These areas were marked by shoreface or deltaic deposits of local origin, usually overlain by shales (Csillag et al 2010). The fauna of these shales may point to water depths of either less than 100 m (Cziczer et al 2009) or few hundred meters (Magyar et al 2004) showing great spatial variations. As the deltaic to alluvial feeder systems from remote Alpine-Carpathian source areas reached these locations, the depositional environment changed, depending on the water depth of the given location.…”

“…Due to lack of any evidence of subaerial exposure or pedogenesis interpretation as calcretes is excluded. Based on analogy of other carbonates of the lacustrine succession (Magyar et al 2004;Cziczer et al 2009) and the algae-like structures it is speculated that these beds formed when carbonate mud accumulated after the bloom of some calcareous algae in the photic zone of the lacustrine water mass. Siltstones point to increased suspension input from distal sources.…”